This invention generally relates to compounds used for the chemical vapor deposition of metal films. In particular, this invention relates to precursor compounds for use in the chemical vapor deposition of aluminum films.
In the semiconductor industry, technological and material development have resulted in the miniaturization, high reliability, high speed, high functionality, and high degree of integration of devices, such as semiconductor integrated circuits. With the development of the manufacturing process of semiconductor devices, the development of improved memory devices, such as dynamic random access memory (xe2x80x9cDRAMxe2x80x9d), has been rapid. Currently, 64 mega DRAM is under mass production and, in the year 2,000, it is anticipated that with the new manufacturing methods of the next generation semiconductor devices, as well as with their mass production capabilities, 256 mega class memory devices may be available, as well as 1 giga (xe2x80x9cGxe2x80x9d) and 4 G class high memory devices.
The next generation memory devices, those having high memory capacity, are the result of miniaturization of the memory device circuits; specifically, narrowing the line widths to 0.25, 0.18, and 0.15 microns (xe2x80x9cxcexcmxe2x80x9d).
The current wiring method in the semiconductor memory devices using aluminum as the wiring material is by vapor deposition, i.e., the sputtering method in which a metal, i.e. aluminum, itself is used for deposition to attain a desired thin film. This method limits the manufacturing process technology in achieving the narrowing of the line width described above.
In the manufacturing of 64 mega DRAM using aluminum (Al) metal wiring, the sputtering method has been the sole method used in the deposition of aluminum from an aluminum target. In the next generation memory devices described above, the circuit line width would be less than 0.25 ,xcexcm and the aspect ratio (depth/diameter) of contact and via hole is large in the vapor deposited metal, thus, the use of sputtering in the vapor deposition process would be unsuitable.
To alleviate such a problem, an aluminum wiring process using chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) method has been studied for a long time. This method has a high step coverage and has an improved burying process of contact/via hole, which is an advantage of the method. Thus, aluminum wiring from vapor deposition of aluminum (xe2x80x9cAl-CVDxe2x80x9d or aluminum chemical vapor deposition) will be the foundation of the technology for the production of the next generation class memory devices and the CVD method is considered to be the imperative method.
In aluminum film deposition using the chemical vapor deposition method, an aluminum compound, known as the precursor, was used as the source material. The chemical properties and the selection of the compound greatly affect the CVD process and they are the most important elements in the process. Therefore, prior to the selection of the deposition method, it is imperative that the selection and development of the precursor are the first factors to be considered.
In spite of the importance of the role of a precursor, the metal film deposition process using CVD method has developed concurrently with the use of the process in the manufacture of the next generation semiconductor devices. For this reason the development of the precursors for Al-CVD has been delayed.
In the early stage of Al-CVD method development, alkyl aluminum compounds were widely used in the industry. The typical alkyl aluminum compounds commonly used were trimethylaluminum, as represented by the chemical formula of Al(CH3)3, and triisobutylaluminum, as represented by the chemical. formula of [(CH3)3CHCH2]3Al.
In the nineteen-nineties, the development of precursors for aluminum film deposition using the chemical vapor deposition process was very active in Japan resulting in the development of dimethylaluminum hydride, represented by the chemical formula of [(CH3)2AlH]2, and in the USA resulting in the development of dimethylethylaminealane, represented by the chemical formula of H3Al:N(CH3)2C2H3. These compounds were leading precursors in the Al-CVD process.
Among the chemical compounds examined, dimethylethylaminealane was synthesized by Wayne Gladfelter of the University of Minnesota, in 1989, after the report of J. K. Ruff et al. in the Journal of the American Chemical Society, 1960. The synthesis of dimethylethylamine, (N(CH3)2C2H3) has not been reported in the complex compound developed from aluminum hydride (AlH3) and an alkyl amine in the report. U.S. Pat. No. 5,191,099 (Gladfelter et al.) discloses dimethylethylaminealane as a precursor in Al-CVD process.
Other chemicals, such as dimethylaluminum hydride, trimethylaluminum, and triisobutylaluminum, have been developed and have been used widely in various applications since the nineteen-fifties. Specifically, dimethylaluminum hydride was reported by T. Wartik et al., Journal of American Chemical Society, 1953, 75, 835, and trimethylaluminum and triisobutylaluminum have been reported quite a bit earlier than the above.
These compounds have been fully commercialized and used in many industrial areas prior to the nineteen-nineties. They can be obtained economically, and they are liquid at room temperature, which are their advantages. However, the above-mentioned compounds have some problems when used as the precursors in the Al-CVD process. The film deposition temperature is above 300xc2x0 C. and near 400xc2x0 C. Due to this high deposition temperature, the vapor deposition process becomes very difficult and the high temperature deposition results in the inclusion of carbon impurities which increase the electric resistance of the deposited film, which are the detrimental flaws.
To alleviate such problems in the Al-CVD process, a dimethylaluminum hydride precursor and related technologies were developed in the early part of the nineteen-eighties. Dimethylaluminum hydride has a high vapor pressure (2 torr at 25xc2x0 C.) and its vapor deposition rate is high and it is a colorless liquid compound at room temperature. Also, advantageously, it provides very pure aluminum film that can be deposited at a low temperature (30xc2x0 C.) when hydrogen gas is used as the reaction gas. However, dimethylaluminum hydride is an alkylaluminum compound that explodes when it comes into contact with air. Therefore, it is very difficult to handle and has high degree of difficulty in the manufacturing process which results in a low yield and high cost.
As alternative precursors in the Al-CVD process, the alane (AlH3) derivatives were used besides dimethylaluminum hydride. One of the alane derivatives, dimethylethylaminealane, forms a vapor deposition film of high purity at low temperature, 100-200xc2x0 C. Dimethylethylaminealane is a colorless chemical compound at room temperature and has a relatively high vapor pressure (1.5 torr at 25xc2x0 C.). In comparison with dimethylaluminum hydride, the flammability is somewhat less and it can be manufactured by a comparatively simple process at a low cost, which is advantageous.
However, dimethylethylaminealane is thermally unstable at room temperature as well as during the vapor deposition process, which is carried out at 30xc2x0 to 40xc2x0 C. Hence, during storage the precursor gradually decomposes in the container. This difficulty in room temperature storage is a disadvantage. For this reason, development and reproducibility of the vapor chemical deposition process has been difficult in semiconductor device manufacturing processes.
It has now been found that certain aluminum compounds retain the advantages of known precursors for aluminum film deposition and solve the problems of these known precursors for Al-CVD applications.
The present invention provides an organometallic compound of the formula
H(Rxe2x80x2)2Al:Lnxe2x80x83xe2x80x83(I)
wherein Rxe2x80x2 is an alkyl or perfluoroalkyl group having 1 to 4 carbons; and L is one or more Lewis bases capable of providing an unshared electron pair to the aluminum and is selected from thiophene, thiopyran or an organic amine of formula II or III 
wherein R is an alkyl having a carbon number of 1 to 4; R1, R2, R21, R22, R23 and R24 are each independently hydrogen (H) or an alkyl group having carbon numbers of 1 to 2; X is oxygen or an alkyl group containing nitrogen; m is an integer from 2 to 8; k and l are each independently integers from 1 to 3; and n is 1 or 2.
The present invention also provides a vapor deposition precursor composition comprising an organometallic compound described above.
The present invention also provides a process for aluminum film formation comprising the step of vapor depositing an aluminum film on a substrate, wherein the source of aluminum in the aluminum film is a vapor deposition precursor comprising an organometallic compound of the formula H(Rxe2x80x2)2Al:Ln; wherein Rxe2x80x2 is an alkyl or perfluoroalkyl group having 1 to 4 carbons; and L is a Lewis base capable of providing an unshared electron pair to the aluminum and is selected from thiophene, thiopyran or an organic amine of formula II or III 
wherein R is an alkyl having a carbon number of 1 to 4; R1, R2, R21, R22, R23 and R24 are each independently hydrogen (H) or an alkyl group having carbon numbers of 1 to 2; X is oxygen or an alkyl group containing nitrogen; m is an integer from 2 to 8; k and l are each independently integers from 1 to 3; and n is 1 or 2.
The present invention further provides a process for preparing an organometallic compound of the formula H(Rxe2x80x2)2Al:Ln; wherein Rxe2x80x2 is an alkyl or perfluoroalkyl group having 1 to 4 carbons; and L is one or more Lewis bases capable of providing an unshared electron pair to the aluminum and is selected from thiophene, thiopyran or an organic amine of formula II or III 
wherein R is an alkyl having a carbon number from 1 to 4; R1, R2, R21, R22, R23 and R24 are each independently hydrogen (H) or an alkyl group having carbon numbers of 1 to 2; X is oxygen or an alkyl group containing nitrogen; m is an integer from 2 to 8; k and l are each independently integers from 1 to 3; and n is 1 or 2, comprising the steps of: a) forming a suspension of trialkylaluminum of the formula Rxe2x80x23Al wherein Rxe2x80x2 is as defined above and lithium aluminum hydride in hexane or pentane; and b) adding to the suspension said Lewis base.
This invention pertains to organometallic compounds useful as precursors in the vapor deposition of aluminum film as wiring on semiconductor devices and methods of preparing the precursor compounds. Specifically, the precursors are useful in the formation of an aluminum metal film layer on a diffusion barrier layer or adhesion layer on a silicon substrate.
Lewis bases capable of providing an unshared electron pair to the aluminum metal center are useful in the present invention Suitable Lewis bases include thiophene, thiopyran, and organic amine derivatives of Formula II or Formula III. For example, the organic amine derivatives include one or more heterocyclic amines selected from alkylaziridine, alkylazetidine, alkylpyrrolidine, alkylpiperidine, alkylhexamethyleneimine, alkylheptamethyleneimine, alkylmorpholine, 1,4-dialkylpiperazine. 
In the above Formula II, R is an alkyl having a carbon number of 1 to 4, R1 and R2 are each independently hydrogen (H) or an alkyl group having carbon numbers of 1 to 2, and m is an integer from 2 to 8. It is preferred that R is methyl or ethyl. 
In the above Formula III, R is an alkyl group having carbon numbers of 1 to 4, R21, R22, R23 and R24 are each independently hydrogen (H) or alkyl group having a carbon number of 1 to 2, X is oxygen or an alkyl group containing nitrogen, and k and l are each independently integers of 1 to 3.
Among the compounds expressed by Formula II, the preferred compounds are alkylaziridines having Formula IV, alkylpyrrolidines having Formula V and alkylpiperidines having Formula VI. Among the compounds expressed by Formula III, the preferred compounds are alkylmorpholines having Formula VII and alkylpiperazines having Formula VIII. 
In the above Formula IV, it is preferred that R is methyl or ethyl and R2 is hydrogen or methyl. It is more preferred that R and R2 are both methyl. 
In the above Formula V, R is an alkyl group having a carbon number of 1 to 4, and R3 to R10 are each independently hydrogen or alkyl group having a carbon number of 1 to 2. Preferred compounds of Formula V are those wherein R3, R4, R6, R7, R9 and R10 are each independently hydrogen or methyl, more preferably wherein R5 and R8 are hydrogen, and most preferably wherein R is methyl, ethyl or butyl. 1-Methylpyrrolidine and 1,4-dimethylpyrrolidine are particularly preferred. 
In the above Formula VI, R is an alkyl group having a carbon number of 1 to 4, and R11 to R20 are each independently hydrogen or an alkyl group having a carbon number of 1 to 2. Preferred compounds of Formula VI are those wherein R is methyl or ethyl, and R11, R12, R14, R16, R18, R19 and R20 are each independently hydrogen or methyl. 1-Methylpiperidine, 1-ethylpiperidine and 1,2,2,6,6-pentamethylpiperidine are particularly preferred. 
In the above Formula VII, R is an alkyl group having a carbon number of 1 to 4, and R25 to R32 are each independently hydrogen or an alkyl group having a carbon number of 1 to 2. Preferred compounds of Formula VII are those wherein R is methyl or ethyl and R25, R26, R27, R28, R29, R30, R31 and R32 are each independently hydrogen or methyl. 4-Ethylmorpholine is particularly preferred. 
In the above Formula VIII, R is an alkyl group having a carbon number of 1 to 4, and R33 to R40 are each independently hydrogen or an alkyl group having a carbon number of 1 to 2. Preferred compounds of Formula VIII are those wherein R is methyl or ethyl and R33, R34, R35, R36, R37, R38, R39 and R40 are each independently hydrogen or methyl. It is more preferred that R is methyl and R33, R34, R35, R36, R37, R38, R39 and R40 are each hydrogen.
Among the compounds defined by Formula II are those wherein the Lewis base is an alkylpyrrolidine. The preferred alkylpyrrolidine is defined by Formula IX. The preferred compounds of Formula IX are those wherein R3, R4, R6, R7, R9 and R10 are each independently hydrogen or methyl. The compounds defined by Formula IX include: 1,2-dimethylpyrrolidine having Formula X, 1-methylpyrrolidine having Formula XI, and 1-butylpyrrolidine having Formula XII. Among the compounds defined by Formula II are those wherein the Lewis base is an alkylpiperidine, having Formula VI, and preferably an alkylpiperidine having Formula XIII. It is more preferred that the alkylpiperidine is 1,2,2,6,6-pentamethylpiperidine having Formula XIV, 1-methylpiperidine having Formula XV, and 1-ethylpiperidine having Formula XVI. 
Among the compound defined by Formula III are those wherein the Lewis base is an alkylmorpholine shown by Formula VII. The preferred compounds defined by Formula VII include: 4-methylmorpholine having Formula XVII and 4-ethylmorpholine having Formula XVIII. Additionally, among alkylpiperazines having Formula VIII, the preferred one is 1,4-dimethylpiperazine, shown by Formula XIX. 
Thus, the preferred organic amines are 1,2-dimethylpyrrolidine, 1-methylpyrrolidine, 1-butylpyrrolidine, 1,4-dimethylpyrrolidine, 1-methylpiperidine, 1-ethylpiperidine, 1,2,2,6,6-pentamethylpiperidine, 4-methylmorpholine, 4-ethylmorpholine and 1,4-dimethylpiperazine.
An aluminum compound represented by Formula I used for aluminum film vapor deposition can be readily prepared according to the chemical reaction represented by Equation 1. Hexane or pentane was added to a mixture of trialkylaluminum (Al(Rxe2x80x2)3), and lithium aluminum hydride (LiAlH4) in a reactor at room temperature to form a suspension and then a Lewis base, L, such as alkylpyrrolidine, alkylpiperidine, alkylmorpholine and alkylpiperazine, was added to obtain the compounds of the present invention.
LiAlH4+Al(Rxe2x80x2)3+nLxe2x86x92H(Rxe2x80x2)2Al: Ln+LiAlH3(Rxe2x80x2)xe2x80x83xe2x80x83Equation 1
In the above Equation 1, Rxe2x80x2 is an alkyl or perfluoroalkyl group with from 1 to 4 carbons, L is a Lewis base, and n is 1 or 2, as defined in Formula I. It is preferred that Rxe2x80x2 is methyl.
Among the Lewis base compounds useful in the present invention, the preferred are 1-methylpyrrolidine and 1-ethylpiperidine. Thus, the typical precursors for the vapor deposition of aluminum film as wiring material in semiconductor device manufacture are the compounds represented by Formula XX, which is 1-methylpyrrolidinedimethylaluminum hydride, and Formula XXI, which is 1-ethylpiperidinedimethylaluminum hydride. The invention will be discussed in relation to these two compounds, namely the use of these compounds as precursors in aluminum film vapor deposition. 
Dimethylaluminum hydride is well known as a precursor in aluminum film vapor deposition, and has been in use since the nineteen-eighties. However, a problem with this compound is its high viscosity and solving this viscosity problem will provide control in attaining a proper delivery rate when a bubbler or other liquid delivery system is used as the transporting system. The ease of the delivery rate control is very important in semiconductor device manufacture. Also important is the reproducibility in the aluminum film vapor deposition process, and such reproducibility allows for the development of aluminum vapor deposition process.
Conventional aluminum chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) precursor compounds, such as dimethylethylaminealane, trimethylaluminum and dimethylaluminum hydride, etc., ignite explosively when they contact water or air. The invention compounds are flammable but they do not ignite explosively or they are less flammable than the conventional precursors, so the risks of fire and personal injury are reduced.
The process of manufacturing the compounds can be carried out with ease and without any danger, yet the yield is high when compared with the manufacturing process of dimethylaluminum hydride. Moreover, the unit production cost will be less than that of dimethylaluminum hydride. Thus, it is expected that the compounds of the present invention would be excellent precursors in aluminum film vapor deposition by using chemical vapor deposition process.
The invention compounds are a liquid at room temperature, and thus, the control of the precursor compound delivery rate, which is closely related to process reproducibility, is easily achieved in the vapor deposition process by using a bubbler. Also, in other chemical vapor deposition processes that use a direct liquid injector or a liquid delivery system, the process can be easily carried out, which is an advantage. In a chemical vapor deposition process, the compounds of the present invention may be vaporized by thermal energy, plasma or a bias applied on the substrate.
Furthermore, as an added feature, the inventors developed precursor compound solutions which are more beneficial than known precursor solutions used in delivery systems such as direct liquid injectors and liquid delivery systems. A heterocyclic amine was used as the solvent for the preparation of a precursor solution for the delivery of the precursor compounds of Formula I, the solute, in a delivery system. Examples of the heterocyclic amine solvent include 1-methylpyrrolidine, 1-butylpyrrolidine, 1-methylpiperidine, 1-ethylpiperidine, 4-methylmorpholine, 4-ethylmorpholine, 1,4-dimethylpiperazine, and the like. It is preferred that the solvent is 1-methylpyrrolidine. The solutes and the solvents are used in various combinations, and the resulting aluminum compound solutions can be used as effective precursors in aluminum vapor deposition processes.
In aluminum film vapor deposition, the invention solutions allow for the development of new processes when compared with that of conventional precursor solutions due to the wide selection of precursors.
Solutions of the above new compounds represented by Formula I were prepared using a heterocyclic amine as the solvent. The new precursor compound solution can be prepared by dissolving the invention compound represented by Formula I in a heterocyclic amine which is free of water, a purified solvent, and a Lewis base. The entire reaction is carried out under an inert gas atmosphere, such as a nitrogen or argon stream, to prevent the deterioration of the compound due to exposure to air.
The invention compounds and the preparation of solutions of the compound will be discussed with examples.